Syntactic Sugar

Temptation: declare logical like this:

        sub logical ($)

Then you could say:

        print logical $struct, "\n";

Don't do this, because then this won't work:

        print logical $struct1, $struct2, "\n"

Instead, fix logical to handle multiple arguments and to return plain strings unchanged.

        sub logical {
          my @args =@_;
          for (@args) {
            next unless ref;
            ...
          }
          return @args;
        }